I disagree with the assessment that he uses an eastern grip. To watch a classic eastern grip, watch Sampras. Even if Fed's FH grip is not a classic semi-western, it is as close to a semi-western as it can be. His index knuckle rests on bevel 4 instead of bevel 2 which is closer to a semi-western grip. His recent error fest is more a problem with him standing close to the baseline and not timing the ball well.

1. GRIP
Many people think Roger Federer plays with a semi-Western grip, similar to Andy Roddick’s. In reality, his grip is closer to Pete Sampras’. Federer keeps part of his hand off the end of the grip, but most of it is still on the back of the handle, directly aligned with the face of the racquet. He shifts his index base knuckle slightly downward about half a bevel toward a semi-Western grip (to do this, stand the racquet on its end, as in the diagram below, and place your index base knuckle between bevels 3 and 4 if you’re right-handed or between 6 and 7 if you’re a lefty). This modiﬁ ed Eastern grip is more conservative than that of most top players, who typically shift farther toward the Western grip and place part or most of their hands under the handle. This grip allows for the ideal contact height for a player who stands close to the baseline and plays the ball early, a key to Federer’s effectiveness.